1. Technical Field
Disclosed herein are methods and systems to implement a physical model, including housing and a gelatinous material therein, and to measure displacements of the gelatinous material in response to a physical force experienced by the model. The model may be used as a surrogate head model to measure brain/skull displacement due to a physical force, such as due to an explosive, ballistic, or automotive crash type of event.
2. Related Art
The U.S. Centers for Disease Control (CDC) defines a traumatic brain injury as a blow, jolt or penetrating impact to the head that disrupts normal brain function. According to a 2006 CDC study, over 1.4 million people sustain a TBI in the U.S. each year. Of those, 235,000 are hospitalized, and 50,000 die.
While leading causes of TBI are falls and motor vehicle accidents, military-related blast injuries are an increasingly important etiology for TBI. According to a 2008 RAND study, approximately 320,000 U.S. individuals involved in U.S. military deployments over the past decade experienced a probable TBI.
Improved interceptive properties of helmets have contributed to increased soldier survivability through the prevention of penetrating injuries. However, the number of casualties exhibiting signs of non-penetrating head injury due to blast exposure has also increased.
Physical models of the human head have been developed to gain insight into blast exposure.
Nahum, et al. (1968), and Trosseille, et al. (1992), performed experiments with post mortem human subjects (PMHS), by attaching pressure transducers and neutral density accelerometers to the skull to measure acceleration of the head and pressures in the brain.
General Motors Corporation developed a device, referred to a Hybrid III anthropomorphic test device (AID), around 1973, to evaluate automotive occupant safety. The device includes a headform having a cast aluminum skull and vinyl rubber exterior skin. The exterior anthropometry of the Hybrid III headform is reasonably accurate from a basic plane upward. Mass characteristics of the headform are similar to those of a human, with replication of rigid body head kinematics. The headform may include instrumentation to measure of linear and angular accelerations in three orthogonal directions. Physical properties of the aluminum skull are not, however, representative of those of a human skull. In addition, the headform does not include a brain stimulant material. Transmission and reflection of a blast wave is thus likely to be dissimilar to that of a human head.
Margulies, (1987), Thibault, et al. (1987), and Thibault, et al. (1990), studied a test fixture having cranial sections filled with silicone gel, and an orthogonal grid placed between layers of the gel. In the studies, the test fixture was subjected to an acceleration pulse. High speed photography was used to capture deformation of the grid, from which displacements and strains could be computed. This technique was also used by Meaney, et al. (1995), in a study to correlate in-vitro tissue modeling with histologic and radiologic evidence of axonal injury to predict regions of injury from experimental and analytical analysis, and (Meaney, et al., 1995).
Hardy, et al. (1996), and Hardy, et al. (1997), used neutral density targets (NDTs), placed within PMHS brains, and a speed bi-planar x-ray system to measure local brain displacement, from which strains could be computed.
Hardy, et al. (2001), used an array of NDTs arranged in two columns in a severed head. The first column contained five or six NDTs and was located in the occipitoparietal region and the temporoparietal region of the brain. A suspension test fixture was used for testing the inverted perfused, human cadaver heads and the test fixture.
Ivarsson, et al. (2006), Bradshaw, et al. (2001), and Ivarsson, et al. (2002), used a technique similar to that of Margulies (1997), by designing a parasaggital model of a human skull made of aluminum and filled with a silicone gel. Within the gel were white markers in a grid-form that, when used with high speed photography, would allow determination of displacements and strains.
Makris, et al. (September, 2000), and Chichester, et al. (May, 2001), used anthropomorphic test devices (ATDs), outfitted with pressure transducers on a head skin surface and accelerometers in the head, as well as pressure transducers and accelerometers on other body parts, to study the effects of blast. The ATDs were in a kneeling position while exposed to different charge sizes.
Bayley, et al. (2004), Bayley, et al. (2005), and Bayley, et al. (2006), used harmonic phase (HARP) analysis of tagged magnetic resonance images (MRI) to determine strains in a gel model, human volunteers, and animal models.
Defense Research and Development Canada, Vulcartier (DRDC Valcartier), developed a device referred to as a Manikin for Assessing Blast Incapacitation and Lethality (MABIL), to evaluate personal protection concepts developed for the protection against blast threats. The device includes a headform formed of solid urethane based on anthropometric data, and includes a pressure sensors in an ear, a pressure sensor in the mouth, and a photodiode in an eye to measure light intensity. The MABIL headform does not include a brain stimulant material and thus does not support measurement of brain-skull displacement.
The United Kingdom, Defence Evaluation and Research Agency (DERA), developed a device known as a Dynamic Event Response Analysis Man (DERAMan). The device includes a head, with a skull and soft gel brain stimulant, mounted to a compliant neck. 40 piezoelectric polymer pressure sensors located within the brain section, 45 piezoelectric ceramic pressure sensors mounted to an inside surface of the skull, two accelerometers, and a three-dimensional force gauge.
Synthetic cortical bone is addressed in Caruso, et al., Development of Synthetic Cortical Bone for Ballistic and Blast Testing, Journal of Advanced Materials, 38 (3), pages 27-36, 2006.